1. Field of the Invention
The present invention relates to technology for watermark-embedding identification information indicating a person who has a right of copyright or the like into digital picture data distributed via various media such as circuits, and relates to technology for extracting identification information from those digital picture data.
2. Description of the Related Art
As digital technology and multi-media public advance in recent years, various data are converted into digital data and are distributed broadly via media such as a communication network, a satellite communication and a CD-ROM (Compact Disk Read Only Memory). When digital data are distributed in this multi-media public, it is not possible to avoid problems concerning copies of digital data.
When a copy of digital data is lawful, it may help the culture in the multi-media public. When, however, the copy is unlawful such as used directly for business, there is a possibility that the copy causes an enormous profit loss for a person who has a right (such as an author, a copyrighter, a copyright holder, a person who has neighboring right) since it is possible to copy digital data without deterioration.
Conventionally, technology is proposed in that identification information is watermark-embedded into picture data in a manner that it is difficult to recognize it by appearances, and the identification information is used as evidence when this picture data is copied unlawfully. For example, the following technology is proposed by J. Cox et al. in "Secure Spread Spectrum Watermarking for Multimedia", NEC Research Institute, Technical Report 95-10. That is, according to this technology, orthogonal transformation is applied to picture data, plural weight coefficients corresponding to dot positions of the identification information are selected among the weight coefficients of basis function obtained by the transformation, dot values of the identification information are respectively added to the selected weight coefficients, and the inverse orthogonal transformation is applied to all weight coefficients including the added coefficients, as the result, identification information watermark-embedded picture data is generated.
In the above-mentioned conventional technology, however, since the weight coefficients obtained by the orthogonal transformation of original picture data (before watermark-embedding identification-information) may be various values, it is not possible to specify weight coefficients to which dot values of the identification information are respectively added among the weight coefficients obtained by the orthogonal transformation of the identification information watermark-embedded picture data. Thus, to enforce the above-mentioned technology, it is necessary to keep and to manage each pair of original picture data and identification information watermark-embedded picture data, and when a copy appears, it is necessary to extract each dot value of identification information by subtracting each weight coefficient obtained by the orthogonal transformation of the kept and managed original data from each weight coefficient obtained by the orthogonal transformation of the kept and managed identification information watermark-embedded picture data and to extract each dot value of identification information by subtracting each weight coefficient obtained by the orthogonal transformation of the original picture data from each weight coefficient obtained by the orthogonal transformation of the copy, thereafter, it is necessary to prove the identify about both identification information.
According to the conventional technology, it is necessary to keep and to manage both identification information watermark-embedded picture data and original picture data twice, therefore, there are problems in that a data management and a proof to detect a copy are troublesome and twice storage are necessary compared with distributed data quantity. These problems are serious, particularly in a database in which data must be updated frequently, such as a database dealing picture data about 1000 pieces and a database for newspapers.
To avoid this twice data management, it is also considered that a part of the weight coefficient obtained by the orthogonal transformation of the original data is permutated by the just value of the identification information. There are possibilities in that this permutation causes a remarkable deterioration of the picture quality after the inverse orthogonal transformation, and in that the identification information is immediately recognized by a reproducer only by the orthogonal transformation of the picture data and then data is rewritten.